Temporal Crustal Structure at 100°E on the Ultraslow-Spreading Gakkel Ridge

While it is well established that ultraslow-spreading ridges exhibit both regions of unusually thick crust and exhumed mantle domains along their axes, the temporal scales governing crustal thickness variations remain poorly constrained, and the processes controlling these long-term variations remain unclear. The Gakkel Ridge, characterized by the slowest spreading rate globally, represents an ideal natural laboratory for investigating such crustal thickness variations. However, the presence of sea ice cover over the Gakkel Ridge poses a significant challenge to conducting seafloor surveys targeting crustal thickness variations perpendicular to the ridge axis, thereby limiting the ability to draw robust conclusions regarding these lateral variations. Here we use high-resolution active-source ocean-bottom refraction/reflection seismic profiling perpendicular to the ridge axis over a 50 km long section at 100°E on the Gakkel Ridge to show the crustal evolution over the past 10 Myr. This study employs 2.5-dimensional first-arrival P-wave tomography to image the evolution of the crustal structure. The results reveal an initial phase of thick oceanic crust (8.5 km) during 0–2 Myr, followed by a transition to thin oceanic crust (4 km) between 2–4 Myr. Subsequently, the period of 4–8 Myr is characterized by the exhumation of serpentinized mantle, before crustal thickening resumes from 8 to 10 Myr. These marked temporal variations in crustal thickness are interpreted as indicative of periodic fluctuations in melt supply. We propose that these variations were driven by mantle temperature perturbations of approximately 30–40°C over an 8-million-year period.